Last year for Mother's Day my son brought home from preschool the most perfect gift a writer and mom could ever receive: a bookmark made from a picture of him. I loved it so much I've been actively looking for a way to do something similar ever since. It was the first thing I thought of this spring when I was looking for an art project for the boys that was more springy, and less, well, Eastery. I still had bookmarks in mind and I remembered pinning this celery paint stamp concept I'd seen…